1. Field of the Invention
The present invention relates generally to protectors for drill pipe and riser joints, and more particularly to pipe end load supports and protectors.
2. Description of the Prior Art
The drill pipe string, in the drilling of onshore and offshore well bores in the oil and gas industry, is typically comprised of a plurality of threadably coupled drill pipe joints. Each drill pipe joint, typically about 30 feet in length, includes tool joints welded to the ends of a drill tube segment. The tool joints have threaded ends to form the threaded connection between the drill pipe joints in making up the drill pipe string. Typically, the tool joint at the upper end has internal threads, commonly referred to as the "box," and the tool joint at the lower end has external threads, commonly referred to as the "pin." When a drill pipe string is made up, i.e., a series of drill pipe joints threadably connected, the downwardly extending pin is stabbed into the upwardly extending box and the connection tightened.
At various times during the drilling of a well, it may become necessary to pull the pipe string out of the well bore, commonly referred to as "tripping out" of the hole. Typically, stands of drill pipe are vertically racked in the drilling rig derrick or mast when making a trip. The term for storing pipe in this fashion in the derrick is referred to as "racking-back pipe" or "standing-back pipe." Presently, pipe is being racked-back up to three to four joints of pipe joined together. Racking-back the pipe saves rig time by sending pipe joints subsea in multiples instead of joint by joint. The usual stand is approximately 90 feet long comprising three pipe joints screwed together. Stands of three pipe joints are called "tribbles." Stands may also be "doubles," comprising two pipe joints screwed together, or "fourbles," comprising four pipe joints screwed together. The stands may comprise drill pipe, casing or tubing.
The stands are racked in a substantially vertical position with the entire weight of the stand resting on the pin of the lowermost joint. It is very important to protect the external threads of the pin against damage so that the joint can be made up when "tripping in" the hole.
It is to be understood that this technique of storing stands of pipe also applies to large diameter casing and risers which may have either threaded ends, flanges or some other couplings, as for example, a slip joint with locking type connectors. Additionally, it is also important to protect both pipe ends during storage and transportation of the pipe joints.
Various types of protectors have been used in the past. For pipes having threaded ends, the past preferred method is the use of a molded thread protector which is either injection molded or pour molded with an elastomeric polyurethane polymer system. The elastomeric polyurethane polymer is a noncellular flexible polyurethane polymer which does a reasonable job of protecting the threads when it is used with a steel shell lined with the flexible polyurethane. Without the steel shell, the flexible polyurethane provides marginal thread protection at best, especially for larger diameter pipes. The load-bearing properties of this type of polyurethane is not sufficient to stand up to the loads generated by standing and storing in a upright position stands of pipe.
As stated above, most riser systems and drill pipe have the pin end down when it is being lowered subsea. Thus, the pin end is the one that normally has the most probability of being damaged due to the amount of weight resting on its end, especially if it is "bumped down" on the rig floor when being moved in and out of storage or use. The pin protectors made of the elastomeric polyurethane can be ruined by the weight of the stands crushing and/or shearing the urethane along its threaded surface or on the bottom of the urethane protector which allows metal to metal contact with the end or sides of the pipe, possibly damaging the threads or the end of the pipe which would prevent a good coupling or seal.
For pipes that have a slip joint with a locking connector or flange connection, the preferred method in the past for large diameter pipe and large diameter pipe having smaller pipes, such as choke and kill lines attached to it, is to fabricate a steel protector which encloses the entire pin end of the pipe and is fastened to the pipe by bolts which are screwed against the outside or inside of the main pipe. On flanged pipe, the protector is bolted directly to the flange. On pipes that are not flanged, the pipes cannot be set on the ends without the possibility of damaging the end because the steel protector can slide on the outside diameter of the pipe and come to rest on the pin ends of the pipe. These steel protectors are usually fabricated from A36 steel and are very heavy making them cumbersome, hard to handle, as well as potentially dangerous to the workers.
It is desirable to have a pipe end load support and protector which is lightweight while having the required strength to withstand the loads to which it is subjected. It is also desirable to have a pipe end load support and protector which is easy to manipulate, install and remove and which is economical to manufacture. It is also desirable that it can be used with pipe stands or with pipe stored or transported horizontally.